1. Field of the Invention
This invention relates to an improved apparatus for making up threaded tubular connections. More specifically, the present invention relates to a manual pipe tong having a handle and jaws connected thereto, and comprising a secondary safety latch which, in the event of a tong failure due to fracturing of the tong jaw segments, keeps the fractured pieces of the tong jaw segments connected together, thereby preventing the pieces from flying outward and potentially injuring workers. The improved tong of the present invention also prevents unintentional opening of the tong jaws, which may occur due to a failure of the tong line.
2. Related Art
Threaded connections are used to join lengths of tubulars in many different applications. Although the ensuing description addresses primarily the use of such tubulars (commonly known as "drill pipe") in the drilling of earth boreholes, such as for oil and gas wells, it is understood that the scope of the present invention encompasses manual tongs used to make up threaded connections on tubulars in any application.
Each section or "joint" of drill pipe typically has an upset at each end, one end comprising a pin connection and the other a box connection. This upset section, commonly referred to as a "tool joint", provides a larger diameter surface which may be readily engaged by pipe tongs, as will be described below.
Manual pipe tongs typically comprise several linked-together and articulated jaw segments (sometimes collectively referred to as "jaws"), the jaw segments pivotally connected to an extended handle, which, as the ensuing description will show, creates a lever for the application of torque to the threaded connection. At least some of the jaw segments contain dies, which are hardened teeth to grip the surface of the tubular to be tightened, such as the tool joints of the drill pipe. The jaws include at least two segments, comprising first and second latch segments, which form a primary latch which permits the jaws to be opened, encircled about a tubular, then latched closed by engaging the first latch segment with a mating part of the second latch segment. Once the jaws are closed about the tool joint, the drill pipe connection is then "made up" by pulling on the handle (which provides greatly increased leverage, as the pull point is displaced several feet from the axis of rotation), usually by a cable or chain connected to a cat head on the rig drawworks, which can provide tremendous pulling force. This operation is reversed to unscrew or "breakout" the threaded connection. The torque required to make up and breakout drill pipe connections is quite high, and consequently the pulling force on the tongs is high, with resulting great stress on the various components of the tong, and in particular the jaw segments.
A large percentage of the major accidents which occur on a drilling rig floor involve failure of the drill pipe tongs, when such tongs are subjected to great stress. A typical occurrence is a catastrophic failure by fracture of a jaw segment, with the result that the tong jaws fly open, come unlatched, and the unlatched and thereby free-flying fragment or fragments thus created (which may weigh, for example, 40 to 160 pounds) flies outward with tremendous force. Any rig worker in the path of such projectile would certainly be injured, and perhaps killed. Catastrophic failures of this nature are minimized by careful design and testing of the pipe tong components before use. In addition to testing, it is further desirable to link together any fragments of the jaw segments created by a failure of one or more jaw segments, so that such fragments remain connected to the pipe tong and cannot fly any great distance away, thereby greatly reducing or eliminating injury and death due to such projectiles.
Some additional number of accidents occur when pipe tong jaws come unlatched when under stress, the pipe tongs then suddenly swinging around under influence of the pulling force and striking a worker. Such unlatching may be caused by a failure of the line pulling the tong. It is therefore further desirable to provide a means to prevent unintentional and undesired unlatching of the pipe tongs.